Current lightning strike protection requirements for fasteners on metallic aircraft stipulate two independent protection measures against possible ignition sources in the tank. Conventionally one protection measure is provided by an insulating anodising/paint layer on the structure, and the other protection measure is to encapsulate the fastener with an over-sealant.
U.S. Pat. No. 7,800,884 describes a device for the protection against electrical discharges of a conductive fixing element of an aircraft, comprising a cap made of non-conductive material and a washer made of non-conductive material insulating the fixing element from electrical discharges.
U.S. Pat. No. 8,092,128 describes a fastener suitable for use in airplane manufacture or repair that is coated with a pre-mixed moisture cure sealant. The sealant layer is coated with a frangible moisture barrier that will break apart when the fastener is installed, thus exposing the sealant to atmospheric moisture. Once exposed to moisture, the sealant will begin to cure.